Queen Elizabeth II officially welcomed Meghan Markle into the royal family during her annual Christmas Day message, just hours after the duchess-to-be was spotted with fiancé Prince Harry, Prince William and a pregnant Kate Middleton attending church service.

The queen, while sitting beside a photograph of Harry and Markle and other photos during a pre-recorded address, said she was excited to welcome new members into her family in the upcoming year. Middleton is also expected to give birth to her third child in April.

Kate Middleton and Meghan Markle talk while arriving for the Christmas service.
(AP)

Markle, who got engaged to Harry in early November, was all smiles during her first public appearance with the queen and members of the royal family. She was spotted walking next to Middleton as she held Harry’s arm while arriving at St. Mary Magdalene Church in Sandringham for traditional Christmas service on Monday.

"[Markle] was very, very lovely," said Judith Wallis, who chatted briefly with the newly engaged couple when they were walking back to Queen Elizabeth’s residence.

Meghan Markle and Prince Harry stopped to talk to people while walking to the queen's residence.
(AP)

Thousands of people gathered outside the church to get a glimpse of the royal family, a larger crowd than previous years possibly because of Markle’s attendance -- it was her first Christmas with the family.

"I suspect there are a few people at home who are thinking, why on earth would I want to leave my nice, warm, comfy house and my nice Christmas presents and stand outside in the cold,” Sky News correspondent Rhiannon Mills said. "But there have literally been thousands of people this morning who have been queuing up to try and get inside the gates of the Sandringham estate. It's been an unbelievable scene, really.”

This was the first time Kate Middleton and Meghan Markle were pictured in public together after the engagement announcement.
(AP)

Elizabeth, 91, and Philip, 96, missed last year's church service because they had the flu, but they seemed in good health during Monday's brief appearance. Philip walked back to the queen's house with other royals, but Elizabeth opted to be driven.

Queen Elizabeth II and members of the royal family attend the Christmas church service.
(AP)

She and Prince Charles' wife, Camilla, rode to and from the service in a chauffeured Bentley with a horse-themed hood ornament, perhaps chosen by the queen, who loves horses and horse racing.

Markle joining the royal family during Christmas was unusual because new members are usually invited to holiday events only after they are married, according to the Telegraph. Kate Middleton was also only welcomed into the family after she married William.

Harry and Markle’s wedding is set on May 19, 2018 at St. George’s Chapel in Windsor Castle.

Remarks pre-recorded by the monarch were televised on Christmas Day in the United Kingdom and the 51 other Commonwealth countries. Elizabeth used her Christmas message to pay tribute to the way London and Manchester pulled together after terror attacks earlier this year. She said it was her privilege to visit young survivors of the attack on a Manchester concert hall as they were recovering from the blast which claimed 22 lives.

"I describe that hospital visit as a 'privilege' because the patients I met were an example to us all, showing extraordinary bravery and resilience," she said.

Elizabeth also paid tribute to her husband, who this year stepped down from most public duties because of his advancing years.

“I don’t know that anyone had invented the term ‘platinum’ for a 70th wedding anniversary when I was born,” she said. “I know [Philip’s] support and unique sense of humor will remain as strong as ever, as we enjoy spending time this Christmas with our family and look forward to welcoming new members into it next year.”

The Associated Press contributed to this report.

Katherine Lam is a breaking and trending news digital producer for Fox News. Follow her on Twitter at @bykatherinelam